1. Technical Field
This invention relates to the area of animal nutrition and pet chews. More specifically, this invention concerns the use of reconstituted rawhide for animal nutrition and pet chews and a method for making the same.
2. Background Art
Rawhide is a primary material for dog chews and is generally made of animal skin, which may be further processed. The material is then dried and cut to size, then rolled, knotted or twisted into a pet chew. Generally, the rawhide material comes from a hide ‘split’; a lower or inner layer of the skin's flesh side that is split away from the upper, or grain layer typically used in leather products. Material for dog chews is generally taken from a lower split that has little remaining commercial value for use in leather products.
Processing animal hide for leather and rawhide products begins with soaking, depilation (called ‘liming’ if lime is included in the process), unhairing, then splitting the hide into layers which are de-limed with acid and bated (to improve suppleness) to result in a pelt ready for tanning. Tanning produces a flexible, more stable form of leather that is less likely to putrefy; whereas rawhide forms inflexible material that becomes putrid when re-wetted. The initially processed animal hide, whether used for higher-value leather grained products, or as rawhide, is referred to as ‘limed animal hide’.
Limed animal hide is generally used in a variety of products, including collagen fiber. Incorporating collagen fiber from rawhide, or combining collagen fiber with rawhide, is well known in the art. Also well known in the art are pet chews made from collagen fiber with or without rawhide that is cut, knotted, molded and/or extruded into various shapes and used by dogs to fulfill their natural chewing behavior.
The commercial production of dog chews from limed animal hide includes the steps of:                Washing: repeated washing with water removes sulfide and lime impurities from the limed animal hide;        Deliming and bating: weak acid materials neutralize lime bound to the limed animal hide; enzymes can be used to further soften and bate the skin fiber structure;        Further washing: repeated washing with water to remove impurities produced in deliming and bating processes;        Swelling with acid or bleach: the specific bleaching agent is determined based on the desired product. To produce rawhide with a natural color, acid can be used to swell the skin and bleach it. After drying, the rawhide will have a transparent appearance. For production of white rawhide, hydrogen peroxide can be used to result in a bleached, white rawhide. Food color can be added to obtain colored rawhide.        Drying: dog chews formed from shaped rawhide are then dried.        
Shaping rawhide chews result in off-cuts and scraps of the rawhide material which are unusable due to uneven thickness, irregular shape, or odd size. These off-cuts and scraps are sold for a lower price than the intact rawhide split. Known techniques to re-process the rawhide scraps for use in pet chews include:                Grinding the rawhide scraps into granules which can then be mixed with gelatin and other edible adhesives. This mixture is then molded by extrusion or injection to form various shapes, or extruded into flat sheets which can be then processed into other shapes such as knotted bones. Disadvantages to this method of re-processing rawhide scraps are two-fold: First, the particles obtained by grinding provide no adhesive properties requiring the addition of gelatin or other adhesive; Second, gelatin, as an adhesive, is hard and brittle after being dried and is therefore difficult to bend and knot into the popular chew shapes.        Producing collagen casings to prepare bonded rawhide. Rawhide scrap pieces are swelled, then gelatinized by mechanical force and extruded or injected into shapes. Disadvantages to this method are again two-fold: First, skin fibers remain expansive when combined with large amounts of water and are therefore difficult to dehydrate. For this reason, material prepared by this method is usually used in the production of thinner products, such as casings made by extrusion molding. Thicker extruded products (such as shaped chews) are difficult to dry, which can lead to high moisture content and a tendency to deteriorate. The second disadvantage is that the resultant product demonstrates a flaky consistency having the tendency to break off during bending and knotting, requiring its use in a shape other than a knotted bone.        
Rawhide dog chews are generally of poor palatability and nutritional value, resulting in the trend of incorporating meat products and infused flavors into the rawhide dog chews. These additional steps increase operational costs for producing the chews. Additionally, a weak bond between the additives and the rawhide limits the application for dog chews.